IDLER GEAR AND BEARING ASSEMBLY
The engine idler gear and bearing assembly, located at the flywheel end of the engine, meshes with the
camshaft and crankshaft gears and rotates on a stationary hub. The hub is secured directly to the cylinder
block by a bolt which passes through the hub and three bolts which pass through the flywheel housing, hub, and
end plate (Fig. 1).
Two timing marks (a triangle within a circle) are stamped on the idler gear diametrically opposite (180 to one
The inside diameter of the idler gear bearing is 2. 186 to 2. 187 inches and the outside diameter of the idler
gear hub is 2. 1825 to 2. 1835 inches. Therefore, the clearance between the idler gear hub and the idler gear
bearing is 0.0025 to 0.0045 inch, with a maximum allowable wear limit of 0.007 inch.
A thrust washer is provided on both sides of the idler gear and bearing assembly. The standard thickness of
the idler gear and bearing assembly is 1. 233 to 1. 234 inches and the standard thickness of the two thrust
washers is 0.236 to 0.240 inch. Therefore, the clearance between the thrust washers and the idler gear is 0.006
to 0.013 inch, with a maximum allowable wear limit of 0.017 inch.
Figure 1. Installing Idler Gear Hub
On an in-line engine, the idler gear is positioned on the left-hand side for a right-hand rotating engine and on
the right-hand side for a left-hand rotating engine as viewed from the rear.
On early engines, an idler gear spacer (dummy hub) was used on the side opposite the idler gear. Currently
the flywheel housing has an integral cast hub and a 0.015-inch thick shim is used between the flywheel housing
and the end plate.
Remove Idler Gear and Bearing Assembly (Flywheel Housing Removed)
1. Remove the idler gear outer thrust washer from the idler gear hub (Fig. 3).
2. Slide the idler gear straight back off of the idler gear hub.
3. Remove the bolt which secures the idler gear hub to the cylinder block. Then remove the idler gear
hub and the idler gear inner thrust washer as an assembly.
Wash the idler gear and bearing assembly, hub, and thrust washers thoroughly in clean fuel oil and dry them
with compressed air. Examine the gear teeth and bearing for scoring, pitting, or wear. If the gear teeth are
worn or the bearing is scored, pitted, or worn excessively, replace the gear and bearing assembly or install a
new bearing in the gear. Examine the outside diameter of the idler gear hub and thrust washers. If scored or
worn excessively, replace them.